Magnetic Resonance Imaging apparatuses (hereinafter “MRI apparatuses”) are apparatuses configured so as to obtain images of the inside of an examined subject with the use of a magnetic resonance phenomenon. Images (i.e., MRI images) that have been reconstructed by MRI apparatuses play an important role in various medical practices such as diagnosing and treating diseases and planning surgery.
When a diagnosis is made regarding the spine as having an intervertebral disc hernia, for example, MRI images are taken on a plurality of slice planes that are positioned parallel to one another along the spine. The plurality of slice planes that are positioned parallel to one another are collectively called a “slab”. FIG. 17 is a drawing for explaining a slab setting process. To set a slab, as shown in FIG. 17 for example, an MRI image (i.e., a sagittal image) obtained by taking an image of the spine of an examined subject on a sagittal plane is displayed as a position determining image, which is used for determining the positions of one or more image taking regions.
Further, within the sagittal image, an operator of the apparatus sets, as shown in FIG. 17 for example, a slab that is made up of three slice planes that are positioned parallel to one another. After that, as shown in FIG. 17 for example, by setting three slabs from the upper part toward the lower part of the spine while varying the angles thereof, the operator determines the image taking regions for the MRI images to be used for making a diagnosis regarding the spine. In this situation, as a method for setting the slabs within the position determining image, a method has been known by which, for example, two points (i.e., a first point and a second point) are sequentially specified in the sagittal image by operating a mouse (for example, see JP-A 2003-290172 (KOKAI)).
According to this method, by using the mouse, the operator moves the cursor to the position indicated by a white dot in FIG. 17 and performs a clicking operation in that position, and subsequently, the operator moves the cursor to the position indicted by a black dot in FIG. 17 and performs a clicking operation in that position. As a result, while using the straight line defined by the two points as a center line, the MRI apparatus sets a slab, based on the center line and slicing conditions that have been set in advance (e.g., the number of slices, the thickness of the slices, and the length of the slices). According to this method, it is possible to change the slicing conditions after the slab has been set.
To reduce artifacts in MRI images, it is necessary, in particular, to set phase encoding directions appropriately For example, aliasing artifacts and flow artifacts are known as artifacts that are caused by the phase encoding direction setting process. FIG. 18 is a drawing for explaining a problem in the conventional technique.
According to the conventional technique described above, for example, each of the phase encoding directions is automatically set to be in the direction from the first point to the second point, as shown in FIG. 18. As a result, as shown in FIG. 18, in the case where the relative positional relationship between the first point and the second point is different for each of the slabs, the phase encoding direction is also different for each of the slabs. For this reason, the operator needs to perform an operation to change some of the phase encoding directions so that the phase encoding directions of all the slabs that have been set become the same as one another.
Further, not only when an image taking region is set by specifying two points, but also when a plurality of image taking regions are set by specifying rectangles within a position determining image while dragging a mouse, the conventional MRI apparatus sets the phase encoding directions along the directions in which the mouse was dragged. As a result, in the case where the moving direction corresponding to the dragging direction is different for each of the image taking regions, the phase encoding direction is also different for each of the image taking regions. For this reason, the operator needs to perform an operation to change some of the phase encoding directions so that the phase encoding directions for all the image taking regions that have been set become the same as one another.
As explained so far, according to the conventional technique described above, a burden is placed on the operator when the operator sets the phase encoding directions for the plurality of image taking regions that have been set within the position determining image.